Torque wrenches, and in particular hydraulic torque wrenches, are well established for use in tightening bolted joints. Such wrenches usually include a hydraulically-operated ram reciprocation of the piston of which causes rotation of an associated crank lever. A ratchet mechanism incorporating means for co-operation with the nut or bolt to be tightened is, in turn, rotated by the lever through drive means reacting between the lever and the ratchet mechanism whereby the nut or bolt is itself rotated.
The application of such a torque wrench to the nut or bolt provides for rotation of the nut or bolt in one direction.
In order to rotate the nut or bolt in the opposite direction, the wrench must be removed from the nut or bolt, turned over, and re-applied to the nut or bolt.
There are situations, for example in the subsea and nuclear industries, where torque wrenches have to be operated remotely, and, in such circumstances, it is not feasible to remove, turn over and reapply the torque wrench to enable the nuts or bolts to be rotated in different directions.
Additionally, torque wrenches are finding uses in many industries as valve actuators where rotation of the valve spindle in both directions must be readily available.
It has therefore been proposed, for example as disclosed in U.S. Pat. No. 2,729,997, to provide torque wrenches incorporating bi-directional mechanisms whereby rotation in both directions can be achieved without removing the wrench from the component to be rotated.
Such bi-directional torque wrenches commonly incorporate a pair of drive shoes each reacting between the crank lever and the ratchet mechanism, one shoe associated with clockwise rotation of the ratchet mechanism and the other shoe associated with anticlockwise rotation of said mechanism.
More particularly, the two drive shoes are interconnected with one another, each shoe being movable between an operative drive position engaging with the ratchet mechanism and an inoperative position disengaged from said mechanism. The interconnection of the two shoes is such that, when one of the drive shoes is in its operative drive position, the other drive shoe is completely disengaged from the ratchet mechanism.
A switching mechanism, which may be manually operated or powered, is provided to alter the relative positions of the drive shoes to achieve either clockwise or anticlockwise rotation. Failure to disengage one of the drive shoes when engaging the other shoe will result in the wrench locking up and preventing rotation of the ratchet mechanism in either direction--the drive shoes will work against one another when both engage the ratchet mechanism.
In the aforementioned subsea and nuclear industries, it is clearly not possible to switch the torque wrench manually, and a remote control arrangement is therefore required.
However, remote switching mechanisms are both expensive and complex to install. For example the wrench may incorporate a hydraulically-operated ram to effect the switching which must be provided with a receiver and a power supply actuated by a remote signal.
Such additional equipment clearly increases the risk of a failure occurring, while the remote nature of the switching operation leads to questions as to whether or not switching has in fact occurred. A sensor could be provided to detect the appropriate movement, but this adds still further to the cost.